1. Field of the Invention
The invention relates to an optical system, in particular of a microlithographic projection exposure apparatus. In particular, the invention relates to an optical system with a polarization-influencing optical arrangement, which is suitable for use in an illumination device or in a projection lens of a microlithographic projection exposure apparatus and which renders possible flexible setting of different polarization distributions, including a mixed tangential/radial polarization distribution.
2. Prior Art
Microlithography is used for producing microstructured components, such as, for example, integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus comprising an illumination device and a projection lens. In this case, the image of a mask (=reticle) illuminated via the illumination device is projected, via the projection lens, onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.
It is established practice to set a tangential polarization distribution in particular in both the illumination device and in the projection lens for the purposes of high-contrast imaging. A “tangential polarization” (or “TE polarization”) is understood to mean a polarization distribution in which the oscillation planes of the electric field strength vectors of the individual linearly polarized light rays are oriented approximately perpendicular to the radius directed at the optical system axis. By contrast, a “radial polarization” (or “TM polarization”) is understood to mean a polarization distribution in which the oscillation planes of the electric field strength vectors of the individual linearly polarized light rays are oriented approximately radially to the optical system axis. Accordingly, a quasi-tangential or a quasi-radial polarization distribution is understood to mean a polarization distribution in which the aforementioned criteria are at least approximately satisfied.
Moreover, there is also a need for setting further polarization distributions which vary over the pupil of the illumination device.
In respect of the prior art, reference is made in a purely exemplary fashion to WO 2005/069081 A2, US 2006/0055909 A1, WO 03/077011 A1 and DE 10 2009 055 184 B4.